This paper proposed a new normalized transform domain conjugate gradient algorithm (NT-CGA), which applies the data independent normalized orthogonal transform technique to approximately whiten the input signal and ut...This paper proposed a new normalized transform domain conjugate gradient algorithm (NT-CGA), which applies the data independent normalized orthogonal transform technique to approximately whiten the input signal and utilises the modified conjugate gradient method to perform sample-by-sample updating of the filter weights more efficiently. Simulation results illustrated that the proposed algorithm has the ability to provide a fast convergence speed and lower steady-error compared to that of traditional least mean square algorithm (LMSA), normalized transform domain least mean square algorithm (NT- LMSA), Quasi-Newton least mean square algorithm (Q-LMSA) and time domain conjugate gradient algorithm (TD-CGA) when the input signal is heavily coloured.展开更多
The Gaussian phase distribution approximation enables analysis of restricted diffusion encoded by general gradient waveforms but fails to account for the diffraction-like features that may occur for simple pore geomet...The Gaussian phase distribution approximation enables analysis of restricted diffusion encoded by general gradient waveforms but fails to account for the diffraction-like features that may occur for simple pore geometries.We investigate the range of validity of the approximation by random walk simulations of restricted diffusion in a cylinder using isotropic diffusion encoding sequences as well as conventional single gradient pulse pairs and oscillating gradient waveforms.The results show that clear deviations from the approximation may be observed at relative signal attenuations below 0.1 for onedimensional sequences with few oscillation periods.Increasing the encoding dimensionality and/or number of oscillations while extending the total duration of the waveform diminishes the non-Gaussian effects while preserving the low apparent diffusivities characteristic of restriction.展开更多
文摘This paper proposed a new normalized transform domain conjugate gradient algorithm (NT-CGA), which applies the data independent normalized orthogonal transform technique to approximately whiten the input signal and utilises the modified conjugate gradient method to perform sample-by-sample updating of the filter weights more efficiently. Simulation results illustrated that the proposed algorithm has the ability to provide a fast convergence speed and lower steady-error compared to that of traditional least mean square algorithm (LMSA), normalized transform domain least mean square algorithm (NT- LMSA), Quasi-Newton least mean square algorithm (Q-LMSA) and time domain conjugate gradient algorithm (TD-CGA) when the input signal is heavily coloured.
基金financially supported by the Swedish Research Council(2022-04422_VR)。
文摘The Gaussian phase distribution approximation enables analysis of restricted diffusion encoded by general gradient waveforms but fails to account for the diffraction-like features that may occur for simple pore geometries.We investigate the range of validity of the approximation by random walk simulations of restricted diffusion in a cylinder using isotropic diffusion encoding sequences as well as conventional single gradient pulse pairs and oscillating gradient waveforms.The results show that clear deviations from the approximation may be observed at relative signal attenuations below 0.1 for onedimensional sequences with few oscillation periods.Increasing the encoding dimensionality and/or number of oscillations while extending the total duration of the waveform diminishes the non-Gaussian effects while preserving the low apparent diffusivities characteristic of restriction.
文摘目的 探讨脑内微出血在腔隙性梗塞病人中的发生率及在脑内各区域的分布情况,以及与其他微小血管病变包括脑白质改变和腔隙性梗塞之间的关系。方法 连续入选腔隙性脑梗塞病人82例。记录一般临床资料、实验室检查及神经精神功能评分包括入院时的美国国立卫生研究院卒中评分(NIHSS)和发病三个月时的Barthel生活指数(BI)和简易精神状态量表(MMSE)。所有病人均进行头颅MR检查观察脑内微出血的数目及部位,脑白质改变的程度和腔隙性脑梗塞的数目及部位。数据处理均采用SPSS软件进行。结果 22例患者(27％)存在脑内微出血,数目由1～42个,分布于脑内不同部位包括皮层-皮层下、丘脑基底节区、小脑和脑干。微出血的数目与腔隙性梗塞的数目以及脑白质改变的程度显著相关(r=0.297,0.552;P=0.007,<0.001)。3个月时微出血组病人的MMSE和BI有低于无微出血组病人的趋势(22.56 vs 24.53,16.71 vs 19.11),但无统计学差异(P=0.162,0.052)。结论 脑内微出血在腔隙性脑梗塞中发生率较高,且与脑白质改变的严重程度以及腔隙性梗塞的数目相关。提示脑内微出血是另外一种微小血管病损的标志,可能代表着更为严重的小血管壁的损害,更为直接地提示出血倾向,在腔隙性脑梗塞的治疗及预防过程中应予以相应的重视。
